Catalyst residue effects on the heterogeneous oxidation of polypropylene

摘要

The chemiluminescence (CL) curves in oxygen from polypropylene with a residual Ziegler-Natta catalyst Titanium concentration ranging from 0.2 to 4.1 ppm were measured from 100 to 150℃ and it was found that the intensity of CL increased and the time taken to reach the maximum CL intensity decreased with [Ti]. The temperature dependence of the time to maximum CL intensity showed an apparent activation energy, E_a, of 88.1 +- 0.6 kJ/mol that was independent of [Ti] but the pre-exponential factor, A′, decreased with increasing [Ti] according to a power law: A′ = 4.7 x 10~(-8)[Ti]~(-0.3). This has been interpreted as reflecting the power law dependence of [Ti]~(-0.33) for the distance between residual particles of catalyst as sites for the initiation of heterogeneous oxidation. This has been tested by stochastic modelling of the spreading of oxidation for a range of volume fractions, p_0, of infectious sites. This modelling allows pseudo-CL profiles to be constructed over the temperature range 100-150℃. The modelling has been restricted to p_0 values equivalent to higher initial [Ti] but the results show that E_a is independent of [Ti] and A′ shows a power-law dependence of [Ti]~(-0.29) consistent with the experimental data.